Precision depth sensor

ABSTRACT

A system and method for monitoring liquid tanks that includes a submersible sensor within the tank below liquid surface. The system may also include a secondary sensor to determine ambient conditions, and a controller to determine when changes in liquid level are due to ambient events, or potential breach of system. A calibration rod may be used to monitor displacement of liquid in the tank and calibrate system to determine changes in height of liquid level.

CLAIM OF PRIORITY

The present divisional application includes subject matter disclosed inand claims priority to U.S. patent application Ser. No. 16/666,183,filed Oct. 28, 2019, entitled “Precision Depth Sensor” (now U.S. Pat.No. 11,274,635, issued Mar. 15, 2022); and to PCT application entitled“Precision Depth Sensor” filed Apr. 27, 2018 and assigned Serial No.PCT/US18/030020, and provisional application entitled “Precision DepthSensor” filed Apr. 28, 2017 and assigned Ser. No. 62/491,882, allincorporated herein by reference, describing inventions made by thepresent inventor.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention is directed to petroleum-based tank sensors, andmore particularly related to storage tank monitoring and maintenance viatesting for leaks in the system.

2. Description of Prior Art

In the retail petroleum industry, it is important to identify andrecognize that underground and aboveground petroleum storage tanks, aswell as other containers such as Under Dispenser Containment (“UDC”) andsumps (to retain leaking fuel, keep water out, contain pumps, access totank probes and sensors, etc.), are not leaking. These tanks, sumps, andUDC's (generally referred to as “tanks”) are usually interconnected bypipe. This means that the tanks, UDCs, and sumps are penetrated (e.g. bythe pipe) at various locations. These penetrations, along withabove-identified used, and the unused, tank top penetrations (bungs), aswell as the fuel vessel itself, need to be monitored and tested toensure the tanks, sumps, UDC's, pipe and other penetrations, as well asthe above describe fueling accessories, are not defective or leaking.Many of the systems of concern are on-site and see relatively minimaluse (as compared to tanks at retail fueling stations).

Identifying Water/Phase Separation

Part of the United States Federal law concerning tank monitoringrequires the detection of ingress of water. As water separates from thefuel (e.g. diesel), or water finds it way in with a fuel delivery, orwater leaks into the tank, this water accumulates at the bottom of thetank. Floats specifically designed to track water at the bottom of fueltanks are common. These floats can rise when the density of the fluid atthe bottom of the container is greater than that of fuel. However, theuse of ethanol in gasoline and biodiesel in diesel have changed theability to detect the ingress of water. These two components, ethanoland biodiesel, both absorb water and mix (or dissolve) well with therespective fuel—thereby modifying the density of the separatedliquid(s). The accumulation of water in these fuels has adverse effectson both the fuel and the storage vessels. The ingress of water isdifficult to detect if it is being absorbed into the fuel.

The accumulation of water in ethanol blends can reach a saturationlevel, or maximum dissolved amount for a specific temperature andethanol content of the fuel. If the fuel temperature falls due to a loadof cool fuel, or temperature equalization with the environment, or otherevent, the ethanol/water (as a mixture that was previously insuspension) can fall to the bottom of the tank. This is known asphase-separated fuel. Immediately upon phase separation, the octanelevel changes (falls) in the remaining fuel due to the loss of ethanolin the fuel. This modified fuel can impair/degrade potential engineperformance, damaging the engine, and possibly ruining the engine. Thephase-separated fuel is more aggressive to the inside of the tanks;steel, coated steel, or fiberglass. This phase-separated fuel is also afeeding/breeding ground for biological and fungal activity within thetank or elsewhere. The biologicals, particularly the Acetobacterbacteria, propagate in this environment. The Acetobacter excretionincludes acetic acid. This acid, and chemical stew, creates what waspredicted and called a “cauldron effect”. The cauldron effect is apotentially aggressive mixture that attacks bare steel, softens thegel/fiberglass coating of steel tanks and of fiberglass lined steeltanks, and is known to expose the mesh, weakening the structuralintegrity of a fiberglass tank such that containment has failed ontanks, steel and fiberglass.

The phase-separated fuel can build up on the bottom of the tank untilphase-separated fuel is close enough to the pump inlet to enter the fueldistribution system and be dispensed into vehicles.

Fuel in the fuel storage tank that is not phase-separated, but is highin dissolved water content, can be pumped into an automotive tank. Thevehicles drive off, and some of the vehicles may be stored indoors.Whether due to storing in cool areas (e.g. A/C garage) or due to storagein outside areas that the temperature cools diurnally, the temperatureof the fuel tank falls to a point to cause phase-separation inside theautomotive fuel tank. Phase-separated fuel begins degrading the fueltank and components in the fuel system.

Water also affects diesel fuels. The accumulation of water in the bottomof a tank provides a fuel water interface that allows microbes torapidly propagate. This interface can grow significant biomass pluggingfilters, a particular type of bacteria (Acetobacter) can acidify fuelcausing tank and equipment degradation.

Most diesel fuel today is mixed with biodiesel to meet Federal fuelguidelines. The Sulphur content is reduced in fuel today. Biodiesel addslubricity to the fuel, a desired addition due to the reduction of sulfurthat used to provide a higher level of lubricity to diesel. Biodieselabsorbs water. Bacteria and molds grow in the biodiesel fuel in part dueto the water in the fuel. The fuel is acidified by the acetic acid wasteof the Acetobacter bacteria growing in the fuel. Bacteria and debrisfall to the bottom of the tank. During a fuel delivery the debris andbacteria are pushed around the tank, up to and including the edges ofthe tank. As the particles are pushed together, chemists recognize thesegroups as colonies. The colonies “slime” themselves, protecting thecolony. This protection increases the survivability of the colony,protecting them from chemical means of killing bacteria in the tank.These colonies excrete acid, concentrating the acid next to the tank ina way that it is not easily dispersed, damaging/destroying steel,softening/damaging the gel coat and fiberglass. Tanks fail in many ways,and may compromise containment of liquid (such as fuel, etc.) storedtherein.

Prior art solutions include magnetostrictive level probes for sensingchanges in fuel level within tanks. Magnetostrictive sensors providehigh resolution level sensors via a magnetostrictive stem float, orprobe level sensor. This continuous liquid level solution is able todetermine level within only a few millimeters. Magnetostrictive sensorswork by using a ferromagnetic metal, which aligns itself with magneticfields. By creating two competing magnetic fields, the magnetostrictivelevel sensor is able to generate a signal denoting the liquid level.

A magnetostrictive probe is built by suspending a ferromagnetic metalwire inside a long stem. Electronics at the top of the stem generate anelectrical pulse that travels down the wire, at regular intervals. Thiscreates the first magnetic field. The second is created by a magnetinside a float that moves up and down the stem with the liquid level.When the electrical pulse reaches the float, and the two magnetic fieldscollide, the metal wire inside the stem twists, and a vibration is sentback up the wire to signal change in fuel level.

There currently exists a need for more careful monitoring, adaptivedynamic monitoring, and monitoring systems that avoid corrosion andother means of adding impurities to the fuel line. Therefore, it isadvantageous to have a small, robust, portable test method that canperform precision tests to detect leaks. Tanks, sumps and UDC's (UnderDispenser Containment) are designed to prevent fuel from polluting thesurrounding area. If the fuel leaves these containments, the ground willbecome polluted, potentially polluting groundwater, potentiallypolluting indoor vapor-space by migrating through soils and enteringbuildings, subways etc.

There is a need in several industries, but notably, the petroleum andthe chemical industry to provide a leak detection method that providesthe ability to integrate several test methods that can reportinformation in several formats, having the ability to test multiplefluids in liquid form.

Therefore a PDS (Precision Depth Sensor) can provide a compact, robustmeasurement device, part of a method to be sure sumps and UDC's and thepenetrations through them are not allowing moisture/water to penetrateinto or fuel out of the containment devices.

It is therefore a primary object of the present invention to providemonitoring of fuel conditions within a tank.

It is another object of the present invention to provide a system tomonitor fuel conditions within a tank.

These and other objects of the present invention will be made clear inlight of the further discussion below.

SUMMARY OF THE INVENTION

The present invention is directed to a method of determining thequalities of a liquid in a storage tank with an embedded sensorsubmerged into the liquid. Preferably, the embedded sensor is set alonga bottom surface of the storage tank, or not more than a two or a fewinches above the bottom surface of tank, preferably about one-half toone-inch or less suspended above bottom of tank, preferably near lowestportion of tank bottom. A displacement rod may be used to calibrate themeasurement via use of a submersion. Conditions may be determined of thetank of fluid via coordinated submerged sensor within the fuel, and asecondary sensor to determine ambient conditions. An initial pressuremay be measured along a specific point in the bottom of the tank. Theweight of the fuel can then be determined based on an initial pressurereading, often along with a measurement of fuel volume. Then one maycalibrate the measurement via use of a submersible displacement rod viasuspending a (preferably vertical cylindrical) rod of a set volume intothe fuel. When the rod is emplaced within the fuel at a specific heightand/or volume, one may detect a new further pressure from the PDSembedded sensor. Thereby, one may determine a change in the pressure asbetween the initial pressure and the further pressure readings. By usinga pressure differential to determine a pressure to volume ratio, one maythereafter monitor the pressure reading at the sensor. Concurrentambient conditions may be monitored simultaneously and in conjunctionwith readings in embedded sensor, such readings to be correlated todetermine if ambient conditions change cause changes in embedded sensorreadings (e.g. as by expansion of fuel due to temperature). Concurrentambient readings may be made within tank (near top (in ullage)), and/orat or near exposed surface above-ground, and/or shallowly buried withinground surface, and/or along exterior surface of tank below ground.

A TCV formula may be used to determine if differences of fluid levelover time are due to natural ambient conditions, or system failure. Theconditions within the fuel are determined by a sunken probe. The probemay rest on the bottom of a fuel storage tank, and/or the probe may restjust above (within an inch or inches) of the bottom of a fuel storagetank. A probe may determine the conductivity or resistance of theliquid, and may compare resistance with the expected change of systemconditions reported by a simultaneous system or outside system sensor. Aprobe may determine the properties of a stored liquid, and compare thoseproperties with the expected change of system conditions reported by asimultaneous system or outside system sensor.

The present invention also includes a system for monitoring the fuellevel in a tank, and determining when changes in the fuel are due toleakage. The system is a precision depth sensor that includes asubmerged sensor below the fuel level within the tank, wherein thesubmerged sensor may include a pressure transducer and a power source,or off-board power source connected via wireless or wires. The systemalso includes a controller for determining or monitoring pressure sensedby the submerged sensor and compare to expected levels. A displacementrod may be used to calibrate the system by moving between a position atleast partially outside liquid in tank, and a position at least morepartially within fuel of tank. Preferably, a secondary sensor outsidethe liquid of the tank, either within tank (towards top, or outside tankmay be used to determine ambient conditions and help coordinatedetermination of the expected fuel level.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with greater specificity andclarity with reference to the following drawings, wherein like numeralsdesignate like parts, and in which:

FIG. 1 demonstrates an underground storage tank with PDS and calibrationrod in alternate positions.

FIG. 2 demonstrates an underground storage tank with PDS and secondarysensor in alternate positions.

FIG. 3 demonstrates an underground storage tank of prior art withmagnetostrictive sensor.

FIG. 4 demonstrates exploded view of PDS sensor.

FIG. 4A demonstrates a cross-section of top of PDS sensor.

FIG. 4B demonstrates a cross-section of center of PDS sensor.

FIG. 4C demonstrates a cross-section of bottom of PDS sensor.

FIG. 5 demonstrates exploded view of PDS sensor.

FIG. 5A demonstrates a cross-section of top of PDS sensor.

FIG. 5B demonstrates a cross-section of center of PDS sensor.

FIG. 5C demonstrates a cross-section of bottom of PDS sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The nexus of the PDS was how to provide a means of measurement of liquidfor different applications, one that did not have the same problems asprior art magnetostrictive probe. Prior art probes typically have ashort lifespan, the cables grow bacteria or corrode, and the resultslose accuracy while testing sumps. Tanks, particularly tall tanks,provided very low resolution due to tank size and mounting issues of theprobes. The corrosion and particulate issue of the prior art is aproblem for the magnetostrictive probe.

One application may include digitally provided a means of line testing,recording the information electronically in real time, without requiringa human to make readings by sight, entering the info and thencalculating the results.

The PDS, as presently described. Provides a higher resolution, allowsmonitoring smaller liquid level movements, for regular tank testing andsump testing. Technology has now advanced with smaller, faster, portablecomputers and higher resolution ADC devices, to allow the PDS device tobecome a viable technology.

A housing protects the electronics as the PDS sensor is submersed. ThePDS system provides a program to record appropriate information andtransmit it to provide calculations.

The use of a temperature-controlled volume to determine: whether changesin volume of the fluid are impacted by ambient conditions, and adjustingexpectations accordingly.

The present application continues on the disclosure of U.S. patentapplication Ser. No. 16/666,183, filed Oct. 28, 2019, entitled“Precision Depth Sensor” (now U.S. Pat. No. 11,274,635, issued Mar. 15,2022), and the incorporated file wrapper, and attachments includedherewith, herein incorporated by reference.

Measuring Leaks

The primary method to determine the integrity of the portion of the tankholding liquid in retail fueling stations is via the use of probes.These probes are combined with a computer/controller/processor, a.k.a.monitoring system. The computer processes signal information from theprobe to establish the liquid level height and fuel temperature insidethe storage tank. This liquid level information is compared to tankcharts (preferably stored in the computer) to establish the fuel volumein the storage tank. The temperature information is used to calculatethe volume change of the fuel due to thermal expansion or contraction ascalculated Temperature Compensated Volume or TCV:

Fuel volume×Temperature change×Coefficient of expansion=TCV

Leak rates are calculated by the results of TCV and time. The testing ofthe area of the tank that does not have liquid is tested in othermethods not addressed here.

The calculated change of fuel volume (fuel volume plus or minus the fuelvolume change from the change of temperature) is compared to themeasured fuel volume (height). If the equipment is accurate, and thecalculations are accurate, and the tank charts are accurate, the TCVshould equal the tank volume. Therefore, TCV should accurately track andcompensate for changes in liquid temperature and/or volume. Changes involume can also be caused by leaks out of the tank, and/or due to theingress of liquid (usually water). It is also possible to compromisesystems when the tank is sitting in an area that retains liquid (such asclay), that effectively makes a containment area (soil or substrate)that water or fuel moves very slowly into and out of. This containedliquid can move in and out of leaking tanks and compromise purity ofcontained fuel.

Prior art solutions include magnetostrictive probes, as seen in FIG. 3.A well-known issue with magnetostrictive probes is stickage. Stickage isthe effect of friction between the stick portion and the float portionof the probe. This problem is exacerbated if the probe is not straightup-and-down (vertical). Stickage is a significant issue when sumptesting is done with magnetostrictive probes as the setup requiresstrict attention to ensure the probes have the least amount of friction.

Another issue with tanks and magnetostrictive probes, is the higherincidence of significant bacterial growth, including bio-film. Thebacterial growth (mostly the Acetobacter, but others contribute to thisproblem) is increasing acidity (lowering pH) and thereby destroyingequipment (including tank surfaces) and increasing friction. Biofilmcontributes to stickage, fouling of the stick/float interface.

Another issue identified with the increasing acidity of fuel is theamount of particles in the fuel due to the corrosion occurring insidethe tank system. The corrosion is continually “stirred” and lifted intothe fuel every time the tank takes a delivery. These particles arecontributing to the float sticking problems. The high acidity is eatingup the containment of the float sensors, rendering them less accurate ornot functional. To combat issues of acidity, the PDS uses 316 stainlesssteel (as is known in the art) for wetted portions of the sensor, suchas the shell or cylinder and caps, and treatment for steel componentsimmersed in low PH fuel allowing long life in low PH fuels.

Calibration

It is important to have a Pretest or Diagnostic mode for sump and othercontainment testing. Today, testing equipment has a Pass/Fail method ofreporting leaks. This is due, in part, that there is no acceptable leakrate allowed if it is detected. Currently, manufacturers use themandated test threshold (such as 0.05 mph for tanks) or ⅛″ per hour (forsumps) as the reporting threshold. Basically, any leaks below thethreshold do not have to be reported, therefore the equipment is notdesigned to report it (either because it lacks sensitivity, or isprogrammed as such). When a technician is testing a tank or sump andthere is a fail, failure could be due to one or multiple failure pointsbelow the threshold of detection required. If there are multiple pointsof failure, there is no tool to help the technician as to where theselevels or failure points are located. Such is the need for a Diagnostictest, a tool that allows technicians to test levels of containments tofind out if it is leaking a proportional share of the total leak.

In order for such a tool to be useful for Pretest or Diagnostic Mode,the sensitivity must minimally meet the ability to detect a proportionalamount of the potential leak points. The PDS and sump test software issensitive enough to detect as small as 0.0000001″. As currentsumps/containments do not normally exceed 10 penetrations, the PDS issuch an appropriate tool. A variation of the PDS can exceed even greatersensitivity as described below, such as to detect 0.00005 gph or0.000005 gph, depending on the size of the sump/tank the PDS is testingin.

Such a tool must be sensitive enough to give accurate information todetect leaks smaller than the aggregate of the leak threshold. It issuggested that in order for such a tool to help identify small leaksthat could in total affect aggregate test results, it should be able toidentify small enough leaks such that if each penetration was leaking aproportional amount, the test equipment could identify each leak,allowing the successful repair of the containment. Each leak could berepaired, in turn, while a test is made after each fix, until nodetectable leaks remain. The Precision Depth Sensor combined with theappropriate software is such a tool for the retail petroleum industryand the current US EPA test thresholds as the penetrations in sumps thatcould leak.

Calibration Feature Example

PDS is placed in a tube of a known depth, such as 2 ft. Fill the tube tothe top, such that excess liquid runs down the side into a secondarycontainer. The weight per distance (height) is then determined. Withweight of a predetermined height, we can now know precise height/weightchanges. This will allow us to measure depths on fluids not in apre-defined list or of an unknown product.

Track the temperature change of the “unknown” fluid in the samecontainer. Weight per degree can be calculated so temperaturecompensated volume testing and monitoring can be accomplished. Ideallythis would occur in real time so the testing and the temperature changecould be identified as the liquid level change is recorded.

Additionally, where the fuel is in a container that allows changes involume and growth due to thermal expansion or thermal contraction to betracked, The COE (coefficient of expansion) could be calculated in thefield, parallel to the testing that is ongoing. The addition of acalibration rod to this container is an additional method to check thesensitivity and accuracy of the information.

Due to equipment, pipes, plumbing, sensors, pumps, leak detectionequipment, etc. the surface area of a sump is not the same as thesurface area calculated of (empty) rectangles, squares, or circles, thetypical shapes of sumps. Therefore, a method that allows an operator tocalibrate the surface area allows the operator to report leak rate asthe depth changes and the surface area allow the test system to reportvolumetric leak rate changes.

PDS embedded sensor should be ai a fixed position in tank. Sensor may belocated in a fuel pipe (drop tube). The drop tube being sealed at a topmay only be affected by ambient conditions. Ullage pressure and ambientpressure should be isolated (and may differ), allowing for more accuratereadings.

The sensor should be set in a fixed position (as in other embodiments)and cannot be loosely suspended to allow random movement of sensor thatmay affect readings (unless location known). If material of sensor willmove, or change size (as in a metal that expands/contracts withtemperature, etc., such information is to be calibrated. The presentsystem may include a pressure temperature monitor over a predeterminedtime. Static temperature within tank may be required to run tests. Onemay make multiple readings over time to detect a leak. Once may comparevaried readings to determine a leak and leak rate. For instance,consecutive readings may not be compared, but a staggered comparison maybe needed (e.g. comparing first and third reading with second andfourth, third and fifth, etc.).

For example, if after the setup of the equipment, including thedeployment of a PDS in the bottom of a tank, a calibration mode in theattached computer was entered, a solid displacement rod of a knownlength/volume could be lowered into the tank liquid, as can be seen inFIG. 1. The calibration reading finishes. The rod is removed. Thisdisplacement of a known rod volume allows the surface area to becalculated based upon the detected height level (weight) change. Tank 1is placed within substrate or soil or ground 2. Tank 1 includes fuel 6with a top level 7. Sensor (PDS) 5 capsule, is preferably a cylinder, orcapsule, or other structure. Rod 3 may be started at position 3 abovelevel 7, and then lowered into fuel 6 at rod position 4. Both rods areshown for illustrative purposes of the position of a single rod. Thevolume of rod immersed is determined by the amount of fuel displaced andheight of fuel, or vice versa. Sensor 5 may record weight, pressure, orthe like. Sensor 5 may also determine temperate, electricalcharacteristics, etc.

The lowering of the displacement rod into the product at beginning ofthe test for calibration, then removing it, and repeating the test atthe end by lowering the calibration rod into the liquid for a secondcalibration and removing it a second time would provide a second datapoint for calibration sensitivity that can be used to confirm thesensitivity, check if the values match, and if not within a statisticalvalid range, indicate the surface area has changed or some othervariable has changed thus requiring compensation of other variables or aretest.

The lowering of the displacement rod in the beginning of the test to geta calibration and leaving it in the liquid during the test, removing thecalibration rod at the end of the test also provides two data points tocalculate surface area/volumetric changes and provides a check to insurethe quality of the data from start to finish.

The parameters of the vessel such as shape and size affect the rate ofchange. For example, in liquid level change detection, if a vessel werelarger on the bottom but the sides sloped inward towards the top of thevessel, the rate of change would slow down as the liquid left thevessel. The liquid level change per time interval would be less for thesame volume of fluid that leaves a vessel with the described slopingwalls verses a vessel that the sides did not slope. A means ofdetermining this change and compensating for this type of variable wouldbe beneficial to reporting accurate rate results.

Similarly, the above-mentioned sloping walls change the accuracy ofvolumetric reporting unless there is a method of determining how thesurface area of the tank is changing and integrating that into thevolumetric calculations or liquid level rate reporting.

Entering a slope calculation mode would allow the use of a displacementrod entered 3 times, once to establish a starting surface area, thesecond would establish a slope, percent change of a consistent slope,the third would either represent the continuation of the same slope, ora different value would represent either a leak, an ingress, or a changeof the slope. The time between Calibration 1 and 2 and 2 and 3 must bevaried by at least two times to differential slope and leak and sloperesults.

Not all exercises test the same material. For example, one system mayhave water as the test media, in another tank, diesel, yet anotherpremium gasoline. Additionally, there may be a different exercise thattests for both water and hydrocarbon, but only in the liquid phase andnot as suspended particles as in determining the volume or percentage ofwater suspended in a hydrocarbon such as diesel fuel.

Calibrating an Unknown Liquid

A user can enter a precise measurement of the current liquid depth.Using this information, we can back calculate the weight per fluid unitat one temperature. A calibrated fluid can be used for precision testingat one temperature. Without a coefficient of expansion (COE) we can onlyapproximate actual fluid depths during temperature change. With severalrepeats of the current liquid depth as above and a new/changingtemperature it is possible to closely approximate the COE for thetemperature.

Dual Sensors

To ensure that the testing system is calibrated correctly, dual sensorsmay be employed. As can be seen in FIG. 2, Tank 1 includes contact withsurface 20, such as through a bung hole. First PDS sensor position 5 maybe at a location just above the bottom of tank 1. Alternative position 8for sensor, may be along bottom of tank. A wire 11 may be used to powerPDS or otherwise transmit analog or digital signals to outside box (notshown). A second sensor location 10 may be used to determine ambientconditions, such as temperature, humidity, etc. A further alternativelocation 9 for secondary sensor may also be used on surface, or outsidetank system. Both secondary sensors 9 and 10 may be used, or each may beused in isolation to support PDS submerged sensor 5. Further alternativelocation 9 may include an interface box, as described below. Connectorwire 19 may pass through bung cap 29 to electronically andcommunicatively connect with embedded sensor.

For instance, weight, height, and/or volume, etc. of the liquid in thetanks is monitored. At the same time, a separate monitor of ambientconditions may be used to monitor the conditions of the greater system(i.e. atmosphere and geographic location). For instance, if as the testis running (or the system is being monitored) the ambient atmosphericpressure may change (i.e. barometric pressure, temperature, dew point,humidity, etc.) thus resulting in a change to the properties of theliquid that may impact one or more of the monitored variables. Bycorrelating the instantaneous data from a sensor within the liquid toanother senor outside the liquid (for instance in the ullage of thetank, above ground, or elsewhere) changes in the fluid due to ambientconditions can be controlled. Therefore, changes that exceed expectedresponse to ambient conditions may indicate a leak.

A first sensor may be placed to gauge atmospheric pressure above groundor in the ullage. A second sensor may be submerged within the liquid thetank (such as an underground storage tank, or above-ground storagetank). Both sensors may be connected in real-time to correct for sensorreadings in the tank. Otherwise, the readings can be matched up at alater time, or in the analysis, to compare atmospheric pressure withreadings in the tank to eliminate false triggers or masked leaks (falsenegatives and false positives).

Simultaneous data may be taken inside, and outside, the tank to test theweight of the fluid and ensure that it meets standards. Weight isdetermined by pressure on the submerged sensor. This data is comparedwith tables for standard compliance, with the additional data point oftemperature.

Another embodiment of the present invention includes a test to determinequantity of water diluted in the fuel. This will help determine therisk—level that the water admixed in the fuel may separate given a majoror minor change in conditions. For instance, if the water level mixedinto the fuel is at the point whereby a drop of ten degrees to fortydegrees in temperature will often cause phase separation (i.e. whendispensed into a vehicle fuel tank which may then be garaged or left outovernight), the system can indicate potential risk of future phaseseparation. Phase separation can occur wherein water drops from diesel,or ethanol/water mixtures drops or separates from ethanol modifiedgasoline. Current systems using a second, lower float (as can be seen inFIG. 3) may work between phase-separated diesel/water, but may not workin gasoline or gasoline/ethanol mixtures. Such a test may be conductedvia determination of electrical resistance through the fuel, forinstance via a probe with two separated terminals and running a voltagethere between. Such an electrical sensor can also determine if thesensor is sitting in phase-separated fuel—based on the resistancebetween the terminals.

Use of electrical current to determine resistance, and thus propertiesof the fuel, may be conducted via a permanently affixed probe. Thisprobe may determine the ongoing risk of phase separation (such as withexpected or potential temperature drops, changes in conditions, orpost-dispensation to vehicles. The probe, or any electrical resistancemeasuring system, can determine the amount of water in the fuel. Thenovelty of the present invention is the use of such a probe in a workingtank, including tanks and an underground storage tank at, for instance,a retail fuel dispensary (gas station).

PDS provides for a more accurate reporting of fluid depth in tall/hightanks via use of multiple sensors. Finding level/leaks in large aboveground storage tanks is difficult, the resolution is much greater if youare measuring tanks 15 ft. and under. One of the issues is the scale orsensitivity of the measurement devices. The same graduations areavailable in the devices used whether you are measuring 15 ft. or 125ft. While time may allow a means of looking for change, it is impossibleto achieve the same resolution with the magnetostrictive or pressuresensitive instruments currently used if you are having to expand thesame scale you used for resolution over 15 ft. and apply it to 125 ft.Because Depth/pressure sensors/pressure transducers (magnetostrictiveprobes also) have a resolution scale, the distance or weight thatsensors are used for (pressure or distance range that is to be parsed)sets the precision that can be obtained. If multiple depth ormagnetostrictive sensors are used, say mounted on a rod or to precisiondistances from each other, the precision of smaller set depth/weightranges could allow significantly higher precision results, allowingalmost any desirable precision by the placement/scale chosen. Allowing apressure overlap, a controller could decide which sensor wasread/reported. The overlap would be to allow each sensor to work withinits range and the desirable sensitivity such that one is no longerread/reported as the pressure range leaves the assigned parameters ofthe defined area of the sensor above or below the specific pressure theintended sensor is depended upon for accurate information.

PDS allows a system to be Diagnosed, not only Tested. Diagnostic isdifferent from Testing from a regulatory perspective in that a Fail isan actionable item from a regulatory perspective. A Diagnostic modeallows sumps and other containers to be checked before a regulatory Testmust be performed. An example would be the need to repair a fitting orconnector that has obviously failed, then check the sump to see if yourrepair is “holding” or working as desired. The repair may not be the topfitting, so the sump may be tested at the level of the penetration, thisis not Testing all the penetrations. Additionally, a Diagnostic may berun after a sump has failed. Detecting at what level the leak is locatedmight entail testing from the top down or bottom up, each penetration,the effects of height (pressure) determining the use of each or bothmethods of testing.

It is well known that determining the height of a fluid can be obtainedby measuring the weight of a fluid (from a point such as the bottom of avessel) given certain known parameters such as: the fluid weight(density) at a specific temperature; temperature of the fluid; pressureon the fluid—Such as barometric pressure, etc. To determine change offluid height it is important to: know elapsed time from one reading tothe next (or the time of a Beginning/Ending Test cycle); know thetemperature of the fluid at the measurement intervals; know the pressureon the fluid when the measurements are made (barometric or other); andcompensate for changing temperature and pressure on the fluid duringmeasurements

The PDS is a digital submersible pressure sensor, as can be seen in FIG.2. As can be seen in FIG. 4, the electronics and sensors should be inenclosures that are water tight, except for the opening of the sensormeasuring pressure. The enclosures are preferably round. The enclosureis preferably lowered to the bottom of a tank or containment sump usingits data cable. The sensor is preferably powered by very low voltage. Abattery may be used to allow the PDS sensor to remain submerged withoutwiring required. The PDS sensor could communicate via wireless to areceiver either at top of tank (either along a second internal tanksensor, or near the bung), or outside of tank system. Alternatively, thePDS submerged sensor can be connected to the tank, and may receive powervia current in an electrically conduction along a metal tank surface.Alternatively, the PDS sensor may be mounted onto a specialized tanksurface near bottom of tank, either along surface of tank or a fewinches above the surface and receive power there through. While the term“along” herein denotes either adjacent (such as resting on bottomsurface of tank) or set just above the bottom surface of the tank, theuse of a multiple of sensors wither resting along the bottom of the tankand/or set just above the surface (and sunk/enveloped by liquid fuel)may be used wherein each of the sensors is separated from another by apredetermined distance (e.g., six inches to two feet). The array ofsensors thus deployed may provide alternate readings of pressure, usefulfor instance, when a significant buildup of water or other precipitateinterferes with other sensors. In a tubular/cylindrical tank, the arrayof sensors may be set along the lowest point, or more preferably oneat/above the lowest point, and other(s) along the curvature slightlyraised from the lowest point of the structure. PDS sensor may sit atbottom of tank, or alternatively be suspended floating at a known heightwithin fuel. A thin wire may be used to provide power to PDS sensor fromoutside tank system to provide power from a small battery, and/or solarcell power source. Preferably, a low-voltage supply is provided to PDS.

The PDS sensor enclosure (or PDS) is used to encapsulate the buriedsensors (within the fuel). The enclosure may include an opening to allowthe fuel weight to be on the transducer. The transducer is soldered tothe board within the sensor. The ADC (Analog Digital Converter) ismarked on the board. Preferably the ADC is in very close proximity tothe pressure sensor connect. Preferably, the pressure sensor connects tothe ADC, the ADC through to the processor. The processor board may sitabove the PCB, the connections through the black ovals to the left andright of the oblong area marked that the ADC and RS-485 is in.

While this is the current configuration, alternative configurations mayinclude circular boards that stack on top of each other in severallayers within sensor. In such an arrangement, the pressure transducer incommunication with the liquid in the sump or vessel can be on one end.The transducer connected to the ADC, to the processor and terminatingwith a liquid proof seal that allows RS 485 communication to theinterface box. The interface box contains a means for the pressuresensor to read ambient air pressure and communicate back to theprocessor in the liquid, allowing compensation for weight of the airpressure pushing down on the liquid we are testing. The interface boxmay also allow multiple PDS's within the same tank, or networked tanks,or multiple unrelated tanks, to communicate to the computer through aUSB connection. The interface box may be a USB hub for the sensors and ameans to provide pressure to the individual PDS sensors. It alsoprovides the “key” for the sensors to communicate with our program.

The “Board or boards” are located in the PDS, mounted longitudinally inthe circular PDS. The PDS sensor may be connected by tube/wire to apoint at top/inside tank, or outside of tank through bung. In sumpdeployments, the top may be open, so the connection would be straightthrough to the interface box, to the computer. Used to monitor a tank,the connector from the PDS would pass through a bung that has a cap thatallows the wire to pass without allowing vapor out or liquid in to thetank. Such sealing could be through already existing compressionfittings, or through a plug that is mounted in the cap with vaporbarriers, that allow connections to be made on both sides of the cap,passing the appropriate information through said connector.

The PDS sensor, using pressure and temperature measurement, can allowdetermination of a temperature compensated level and/or TCV. Temperaturemay be measured from a sensor embedded in the housing liquid path(s),and/or elsewhere within tank, and/or outside of tank system. Free water1″ in depth can be detected with an intrinsically safe water detectioncircuit. Entrained water in fuel can be detected with an intrinsicallysafe water detection circuit.

All data conversions, filtering, and timed testing are performed in thePDS, an advantage as the potential of passing data that is corrupted bytransmission errors or missed communications at the receiving equipmentis reduced. The PDS communicates to a computer or controller over anintrinsically safe cable or through intrinsically safe wirelesscommunications. Level may be reported to at least 0.0005 resolution.Temperature sensitive to 0.01-degree F. The sensor should be able topass through a 2″ NPT threaded opening for temporary deployments. Theunit may be able to be calibrated to unknown liquid types.

Currently, no permanently installed or temporarily installed liquidlevel sensor used in the petroleum industry can also report entrainedwater levels (above ASTM standards for the liquid such as ASTM D6304-07,reporting 500 ppm or more water in diesel fuel or ASTM D6304-07 forgasoline, reporting 1,500 ppm water in gasoline). The addition offinding and reporting free water levels as low as 1″ with entrainedwater, with a petroleum or other liquid level depth sensor is also notcurrently available in the prior art.

The present invention also includes the optional use of electricalconductivity, ohms or resistance, to determine the amount of water infuel. While this is a test performed in labs, no one has combined itwith a liquid level monitor to monitor fuel level/volume and suspendedwater, and free water, especially via two integrated methods ofmonitoring.

To determine the size or capacity of the tank, in tank gauging, or intank testing systems, different tank configurations are resident suchthat an operator can enter length and width and height measurements ofcommon dimension tanks of various configurations including square,oblong and round tanks that are horizontal or vertical. The tables forround, square, horizontal and vertical tanks show inches/volumes toaccount for changes of volumes as the diameter of the tank changes.There are charts that account for differences of the ends of tanks asfiberglass and steel tanks have different volume changes as the ends ofthe tanks are different. For instance, steel tanks have mostly flat endsand fiberglass tanks have a significantly larger bell on the end.Similarly, dimensions of a sump can be manually entered to calculatesurface area of a sump. Such methods are acceptable and commonly used.However, there are more automated ways that are more accurate and allowsumps that have difficult shapes or protrusions to determine surfacearea.

If the vessel has pipes or equipment inside the area to be tested, andthe equipment or pipes are exposed. The volume of the liquid in the sumpis not easily calculated.

The present invention includes a test method with:

-   -   a. The ability to test a wide variety of vessels: vertical,        horizontal, round, oval, sumps, drums, transport tanks, etc. to        determine if there are leaks. The shape, dimensions and        protrusions of and in the tank affect accurate volumetric        reporting. Due to equipment, pipes, plumbing, sensors, pumps,        leak detection equipment, etc. the surface area of a sump may        not be the same as the surface area calculated of (empty)        rectangles, squares, or circles, the typical shapes of sumps.        Protrusions in tanks Therefore a method that adds or subtracts        known volumes can be used to “calibrate” a specific volume        displacement to change in height to determine the volume change        in tanks that have irregular shapes or protrusions such as        pipes, pumps or other irregular shapes in the tank at the height        of the tank;    -   b. in a vessel, determining the height of a leak from the bottom        of the vessel.    -   c. Testing can be such that level change in a given time is the        desired metric to evaluate an action point or a classification        such as Pass-Fail

It is well known that determining the height of a fluid can be obtainedby measuring the weight of a fluid from a point such as the bottom of avessel given certain known parameters such as:

-   -   The fluid weight (density) at a specific temperature    -   The temperature of the fluid    -   The pressure on the fluid—such as barometric pressure

To determine change of fluid height it is important to: know elapsedtime; know the change of the temperature of the fluid during additionalmeasurements; know the change of pressure when subsequent measurementsare made; and compensate for changing temperature and pressure on thefluid during measurements.

Testing can also be such that a volumetric amount is the desired resultsuch as 0.1 gallon per hour. In order to report in volumetric measures,the parameters of the vessel are important. The shape, dimensions andprotrusions of and in the tank affect accurate volumetric reporting. Dueto equipment, pipes, plumbing, sensors, pumps, leak detection equipment,etc. the surface area of a sump may not be the same as the surface areacalculated of (empty) rectangles, squares, or circles, the typicalshapes of sumps. Therefore, a method that adds or subtracts knownvolumes can be used to “calibrate” a specific volume displacement tochange in height to determine the volume change in tanks that haveirregular shapes or protrusions such as pipes, pumps or other irregularshapes in the tank at the height of the tank.

The placement of at least two sensors to measure fluid in a containerthat is shifting up-and-down from the back-to-the-front. Multipleinstantaneous readings allow instant readings that can be used tocalculate more precise volume readings of tanks in vehicles that aremoving such as ships, planes, cars trucks. A more precise volumemeasurement can be determined in a shorter time by including multiplesensors, but four sensors can give four axis weight distribution.

Field Testing

A PDS has been installed in a test site involving an intermediate tankused to transfer fuel into hospital gensets and boiler loop system. The1000 gal. tank stores fuel for two generators and when needed a back-upboiler loop. Fuel is routinely used in by the gensets and when thereplenishment level is met (70% of tank level) fueling from main tank(s)is sent to refill the intermediate tank to 90%. A routine test run onthe system includes; manually emptying the intermediate tank andinitiating a reset. Upon reset, as the tank control system reboots,detects the low liquid level and initiates a refill to the correctheight, 90%. Detecting accurate tank levels both in normal operation andthrough extensive manual test sequences has shown the PDS to be robustin its function through climate extremes and a robust test protocol.

PDS Operation

The pressure transducer is directly soldered to the printed circuitboard and immediately routed through the 24 bit analog to digitalprocessor. The A-to-D processor outputs directly to the 32 bit processorwhich does all the math and statistics to output the depth and gallonageof the fluid the transducer is testing/monitoring.

The interface box has the external pressure sensor and communicates thatto the PDS for real-time pressure compensation.

This information from the PDS is passed to the PDS interface box via RS485 communication and from the interface box to a computer that has theVMI PDS reporting software. The reporting software may be in a laptopcomputer such that a tester may move from site to site saving theinformation, transmitting the information through such communications asthe laptop is capable of, or printing the information. The PDS may alsobe reporting to a standalone computer at a site that is continuouslymonitoring tanks and reporting Alarms by horn or light, or outputting analarm to tank monitoring equipment designed to communicate alarmsappropriately as the site has specified, or the PDS computer may beconnected to communication systems directly. Such direct connection mayallow remote monitoring and reporting of alarms as well as all real-timedata gathered, including passed test and alarm or reporting levelevents. Such equipment can be configured to allow modification ofprograms to accommodate upgrades or “bug” fixes.

One such application is to allow information to be shared with BuildingManagement Systems that monitor important equipment such as tank fuellevel, line leak detection, overfill alarms, security systems, oxygendelivery systems, heating and cooling equipment, etc.

Such equipment can be connected with other VMI programs to controlpumps, valves, filtration, chemical injectors for bacteria issues, etc.

Global Data Structure variables for calculation of fuel propertiesinclude:

-   -   Current    -   Pressure;    -   Pressure depth    -   Calculated actual depth    -   Internal temperature    -   On chip temperature    -   State    -   Input    -   Calibrated ADC count/mbar    -   IS Modules State    -   Pressure ADC Value    -   Internal Temperature ADC value    -   On Chip Temperature ADC value

The PDS may also have a 24-bit fluid conductivity sensor to allowdetermination of the water % in the fuel. The barometric sensor has a24-bit temperature sensor so TCV can also be very accurate.

One may put the same pressure sensor in the external USB sensor to giveus current barometric pressure. Minus this value from the absolute andwe have actual fluid weight. A 1200 mBar absolute SMT pressure sensormay mount on the PDS PCB. Adding the two values together gives usabsolute measure depth.

A 32-bit processor is preferably used and connected to PDS senorpressure transducer. A 24-bit processor may be connected to theprocessor to provide ADC. Preferably, these items are contained in thePDS sensor item shown in FIGS. 4-5. The system may communicate to a boxvia USB, or other, cable. The box may include a standard computer thatis protected from the elements. Alternatively, a wireless signal may beemitted for control by a management system further away from the tank. Awire, or wireless, communication system may allow the PDS to communicatewith a computer, such as a laptop, that runs software capable ofproviding output to a user. The computer may also include memory torecord and store data. The computer may also be configured to providereports, alarms, etc. Similarly, a power source (e.g., municipalhigh-voltage line) may be led down into tank to power transducer andother PDS equipment. Preferably, power is transformed to low-voltagewhen entering the tank. The power line may be transmitted along thecable or pole supporting PDS.

PDS sensor 30 is shown. Center cylinder 32 is preferably hollow tocontain circuit board and other onboard components. Top cap 31 may beused to seal PDS, and bottom cap 33 may be similarly used. Transducermay be exposed through PDS sensor surface to allow measurements to betaken. A membrane 37 may expose the transducer to local pressureconditions outside PDS within tank, the membrane may be situated at thebottom or in the sidewall of the PDS shell, or more preferably in thetop cap 31 or bottom cap 33. Emanating wires 36 may read electricalresistance in the fuel, emanating from the sidewalls of the PDS shell.Additionally, wire may communicate information and/or power tocomponents in PDS sensor through shell 32 or top or bottom of PDS.Printed Circuit Board (PCB) 35 may be included and shielded within PDSshell.

I claim:
 1. A method of determining the qualities of a liquid in astorage tank with an embedded sensor submerged into the liquid, with theembedded sensor along a bottom surface of the storage tank or not morethan a few inches above the bottom surface, said method comprising thesteps of measuring the initial pressure along a specific point in thebottom of the tank; determining a weight of the fuel based on theinitial pressure reading; calibrating the measurement via use of asubmersible displacement rod via suspending a rod of a set volume intothe fuel; detecting a further pressure; determining a change in thepressure as between the initial pressure and the further pressurereadings; setting the pressure differential to determine a pressure tovolume ratio; and thereafter monitoring the pressure reading at thesensor.
 2. The method for determining the qualities of a liquid in astorage tank as set forth in claim 1, further comprising the step ofmeasuring an ambient condition via a secondary sensor.
 3. A method suchas in claim 2 whereby the embedded sensor determines the properties of astored liquid, and compares those properties with the expected change ofsystem conditions reported by a simultaneous secondary sensor detectingambient conditions.
 4. A method as set forth in claim 1 wherein theembedded sensor rests on the bottom of a fuel storage tank.
 5. A methodas set forth in claim 1 wherein the embedded sensor rests no more thanone inch from the bottom of a fuel storage tank.
 6. A method such as inclaim 1 whereby the embedded sensor determines the conductivity orresistance of the liquid.
 7. The method as set forth in claim 6 whereinthe embedded sensor compares conductivity or resistance with theexpected change of system conditions reported by a secondary sensordetecting ambient conditions.
 8. The method as set forth in claim 1further comprising the step of removing the displacement rod from thefuel, wherein said step of monitoring comprises taking multiple furtherpressure readings at a set time interval; and comparing the initial,further, and multiple further pressure readings to determine a weightchange of the fuel (based on pressure change reading) to detect a leak.9. A method according to claim 1 further comprising determiningconditions of a tank of fluid via the embedded sensor within the fuel,and a secondary sensor for determining ambient conditions, and utilizinga temperature compensated volume to determine if differences of fluidlevel are due to natural ambient conditions.
 10. A system for monitoringthe fuel level in a tank, and determining when changes in the fuel aredue to leakage, said system comprising: a. an embedded sensor submergedeither along a bottom surface of the storage tank or not more than twoinches above the bottom surface and set below the fuel level within thetank; b. said embedded sensor comprising a pressure transducer and apower source; c. a controller determining pressure sensed by saidembedded sensor.
 11. The system of claim 10 further comprising a soliddisplacement rod moving between a position at least partially outsidefuel in tank, and a position at least more partially within fuel oftank.
 12. The system of claim 10 further comprising a secondary sensoroutside the liquid of the tank, said secondary sensor capable ofdetecting ambient conditions of at least one of temperature, pressure,humidity, and/or dew point.
 13. The system of claim 12 whereby saidsecondary sensor is within the tank, said embedded sensor and saidsecondary sensor connected to a monitoring system.
 14. The system ofclaim 12 whereby said secondary sensor is outside the tank, saidembedded sensor and said secondary sensor connected to a monitoringsystem.
 15. The system of claim 12 wherein said embedded sensor includesan opening to expose the pressure transducer directly to the fuelpressure.
 16. The system of claim 12 wherein said embedded sensorcomprises an analog digital converter coupled to said pressuretransducer, said analog digital converter in communication with saidcontroller.
 17. The system of claim 16 further comprising an interfacebox housing said secondary sensor.
 18. The system of claim 16 whereinsaid embedded sensor and said secondary sensor are coupled via aconnector that passes through a vapor-proof bung cap.
 19. The system ofclaim 10 wherein said embedded sensor is located within or below a droptube.
 20. The system of claim 10 whereby the controller comprises memoryto record and store data, and the controller receives simultaneous datafrom the submerged sensor and data from the secondary sensor.